Field of the Invention
The present invention pertains to semiconductor packaging techniques, and more particularly, high-temperature, hermetically sealed non-axial electronic packages and methods of making.
Description of Related Art
Semi-conductor or integrated circuit devices and assemblies are typically contained in sealed packages to prevent exposure to and damage from their operating environment. Hermetic packages are typically formed from ceramic or metal components bonded together and sealed with glass or metal and are much more costly to manufacture. Non-hermatic packages are generally formed from ceramic, metal or plastic components and sealed with epoxy encapsulants. The epoxy encapsulants are sufficient to seal packages for (High Voltage>600v) silicon chips because the chip will go intrinsic at temperatures around 200° C. Accordingly the epoxy only needs to be capable of withstanding operating temperatures of about 175° C. These encapsulants, however, are not capable of withstanding the higher operating temperatures of the newer high temperature semiconductors, including silicon carbide, gallium arsenide, gallium nitride and diamonds.
Silicon carbide and other high temperature semiconductors, can actually operate at up to 600° C. and in fact operate more efficiently at higher temperatures around 300-400° C., but the current packages sealed with a thermoplastic epoxys fail at 250-300° C., and most are only rated to 175° C. Moreover, the thermoplastic materials do not self fuse or seal to metal as well as a ceramic glass and therefore are not able to provide a hermetic seal.
Axial glass bead packages are made using a glass ceramic compound and thus can operate a temperatures as high the 300-400° C. temperatures optimal for the high temperature semiconductor, but the method of making the glass bead package is only applicable to axial, i.e. single pin out, packages.
In addition, current bonding process for attaching the electrical interconnections between the semiconductor dies and the lead frame uses aluminum wire which would melts into die at higher assembly and operating temperatures required to melt a glass compound.
Thus, it would be desirable to provide a sealing material and bonding process for making semiconductor packages that can provide hermetically sealed packages capable of withstanding high assembly and operating temperatures. It would further be desirable to thermally match the coefficients of thermal expansion for the sealing material, bonding materials, die and other components in order to provide a semiconductor package that is capable of withstanding wide extremes in operating temperature.